Killing Of Acute Myeloid Leukemia Cells Research Articles

Proteasome inhibition enhances the anti-leukemic efficacy of chimeric antigen receptor (CAR) expressing NK cells against acute myeloid leukemia

BackgroundRelapsed and refractory acute myeloid leukemia (AML) carries a dismal prognosis. CAR T cells have shown limited efficacy in AML, partially due to dysfunctional autologous T cells and the extended time for generation of patient specific CAR T cells. Allogeneic NK cell therapy is a promising alternative, but strategies to enhance efficacy and persistence may be necessary. Proteasome inhibitors (PI) induce changes in the surface proteome which may render malignant cells more vulnerable to NK mediated cytotoxicity. Here, we investigated the potential benefit of combining PIs with CAR-expressing allogeneic NK cells against AML.MethodsWe established the IC50 concentrations for Bortezomib and Carfilzomib against several AML cell lines. Surface expression of class-I HLA molecules and stress-associated proteins upon treatment with proteasome inhibitors was determined by multiparameter flow cytometry. Using functional in vitro assays, we explored the therapeutic synergy between pre-treatment with PIs and the anti-leukemic efficacy of NK cells with or without expression of AML-specific CAR constructs against AML cell lines and primary patient samples. Also, we investigated the tolerability and efficacy of a single PI application strategy followed by (CAR-) NK cell infusion in two different murine xenograft models of AML.ResultsAML cell lines and primary AML patient samples were susceptible to Bortezomib and Carfilzomib mediated cytotoxicity. Conditioned resistance to Azacitidine/Venetoclax did not confer primary resistance to PIs. Treating AML cells with PIs reduced the surface expression of class-I HLA molecules on AML cells in a time-and-dose dependent manner. Stress-associated proteins were upregulated on the transcriptional level and on the cell surface. NK cell mediated killing of AML cells was enhanced in a synergistic manner. PI pre-treatment increased effector-target cell conjugate formation and Interferon-γ secretion, resulting in enhanced NK cell activity against AML cell lines and primary samples in vitro. Expression of CD33- and CD70-specific CARs further improved the antileukemic efficacy. In vivo, Bortezomib pre-treatment followed by CAR-NK cell infusion reduced AML growth, leading to prolonged overall survival.ConclusionsPIs enhance the anti-leukemic efficacy of CAR-expressing allogeneic NK cells against AML in vitro and in vivo, warranting further exploration of this combinatorial treatment within early phase clinical trials.

Arsenic trioxide and p97 inhibitor synergize against acute myeloid leukemia by targeting nascent polypeptides and activating the ZAKα-JNK pathway.

Arsenic trioxide (ATO) has exhibited remarkable efficacy in treating acute promyelocytic leukemia (APL), primarily through promoting the degradation of the PML-RARα fusion protein. However, ATO alone fails to confer any survival benefit to non-APL acute myeloid leukemia (AML) patients and exhibits limited efficacy when used in combination with other agents. Here, we explored the general toxicity mechanisms of ATO in APL and potential drugs that could be combined with ATO to exhibit synergistic lethal effects on other AML. We demonstrated that PML-RARα degradation and ROS upregulation were insufficient to cause APL cell death. Based on the protein synthesis of different AML cells and their sensitivity to ATO, we established a correlation between ATO-induced cell death and protein synthesis. Our findings indicated that ATO induced cell death by damaging nascent polypeptides and causing ribosome stalling, accompanied by the activation of the ZAKα-JNK pathway. Furthermore, ATO-induced stress activated the GCN2-ATF4 pathway, and ribosome-associated quality control cleared damaged proteins with the assistance of p97. Importantly, our data revealed that inhibiting p97 enhanced the effectiveness of ATO in killing AML cells. These explorations paved the way for identifying optimal synthetic lethal drugs to enhance ATO treatment on non-APL AML.

CD37 is a safe chimeric antigen receptor target to treat acute myeloid leukemia

Acute myeloid leukemia (AML) is characterized by the accumulation of immature myeloid cells in the bone marrow and the peripheral blood. Nearly half of the AML patients relapse after standard induction therapy, and new forms of therapy are urgently needed. Chimeric antigen receptor (CAR) T therapy has so far not been successful in AML due to lack of efficacy and safety. Indeed, the most attractive antigen targets are stem cell markers such as CD33 or CD123. We demonstrate that CD37, a mature B cell marker, is expressed in AML samples, and its presence correlates with the European LeukemiaNet (ELN) 2017 risk stratification. We repurpose the anti-lymphoma CD37CAR for the treatment of AML and show that CD37CAR Tcells specifically kill AML cells, secrete proinflammatory cytokines, and control cancer progression invivo. Importantly, CD37CAR Tcells display no toxicity toward hematopoietic stem cells. Thus, CD37 is a promising and safe CAR Tcell AML target.

Deep PIM kinase substrate profiling reveals new rational cotherapeutic strategies for acute myeloid leukemia

AbstractProvirus integration site for Moloney murine leukemia virus (PIM) family serine/threonine kinases perform protumorigenic functions in hematologic malignancies and solid tumors by phosphorylating substrates involved in tumor metabolism, cell survival, metastasis, inflammation, and immune cell invasion. However, a comprehensive understanding of PIM kinase functions is currently lacking. Multiple small-molecule PIM kinase inhibitors are currently being evaluated as cotherapeutics in patients with cancer. To further illuminate PIM kinase functions in cancer, we deeply profiled PIM1 substrates using the reverse in-gel kinase assay to identify downstream cellular processes targetable with small molecules. Pathway analyses of putative PIM substrates nominated RNA splicing and ribosomal RNA (rRNA) processing as PIM-regulated cellular processes. PIM inhibition elicited reproducible splicing changes in PIM-inhibitor–responsive acute myeloid leukemia (AML) cell lines. PIM inhibitors synergized with splicing modulators targeting splicing factor 3b subunit 1 (SF3B1) and serine-arginine protein kinase 1 (SRPK1) to kill AML cells. PIM inhibition also altered rRNA processing, and PIM inhibitors synergized with an RNA polymerase I inhibitor to kill AML cells and block AML tumor growth. These data demonstrate that deep kinase substrate knowledge can illuminate unappreciated kinase functions, nominating synergistic cotherapeutic strategies. This approach may expand the cotherapeutic armamentarium to overcome kinase inhibitor–resistant disease that limits durable responses in malignant disease.

The CD33xCD123xCD70 Multispecific CD3-Engaging DARPin MP0533 Induces Selective T Cell-Mediated Killing of AML Leukemic Stem Cells.

The prognosis of patients with acute myeloid leukemia (AML) is limited, especially for elderly or unfit patients not eligible for hematopoietic stem cell (HSC) transplantation. The disease is driven by leukemic stem cells (LSCs), which are characterized by clonal heterogeneity and resistance to conventional therapy. These cells are therefore believed to be a major cause of progression and relapse. We designed MP0533, a multispecific CD3-engaging designed ankyrin repeat protein (DARPin) that can simultaneously bind to three antigens on AML cells (CD33, CD123, and CD70), aiming to enable avidity-driven T cell-mediated killing of AML cells coexpressing at least two of the antigens. In vitro, MP0533 induced selective T cell-mediated killing of AML cell lines, as well as patient-derived AML blasts and LSCs, expressing two or more target antigens, while sparing healthy HSCs, blood, and endothelial cells. The higher selectivity also resulted in markedly lower levels of cytokine release in normal human blood compared to single antigen-targeting T-cell engagers. In xenograft AML mice models, MP0533 induced tumor-localized T-cell activation and cytokine release, leading to complete eradication of the tumors while having no systemic adverse effects. These studies show that the multispecific-targeting strategy used with MP0533 holds promise for improved selectivity toward LSCs and efficacy against clonal heterogeneity, potentially bringing a new therapeutic option to this group of patients with a high unmet need. MP0533 is currently being evaluated in a dose-escalation phase 1 study in patients with relapsed or refractory AML (NCT05673057).

Abstract 6712: LBL-043, a novel LILRB4xCD3 T cell engager, for the treatment of LILRB4 positive leukemia

Abstract Background: Acute myeloid leukemia (AML) is a malignant clonal disorder linked to a broad spectrum of molecular alterations. It is still an incurable cancer, the prognosis is even worse in elderly patients, where overall survival (OS) at 1 year is approximately 10-15%. Now, several CD3 bispecific immunotherapies that harness T cells against AML are at various stages of preclinical and clinical development, but most of them are hampered by the lack of specific targets to distinguish tumor cells from normal hematopoietic stem cells (HSC). Leukocyte immunoglobulin-like receptor B4 (LILRB4) is an immune checkpoint inhibitory receptor, which is highly expressed on FAB M4 and M5 AML cells with a lack of expression on normal HSC and progenitor cells. LILRB4 expression level inversely correlates with OS of patients with M4 and M5 AML. All of these indicate that LILRB4 represents a promising target for developing a T cell redirecting bispecific antibody to treat patients with AML, especially for more aggressive M4 and M5 subtype. Herein a novel bispecific antibody targeting LILRB4 and CD3, LBL-043, is developed to specifically kill LILRB4 positive tumor cells by engaging T cells. Methods: LBL-043 was constructed using our proprietary LeadsBodyTM T cell engager platform, which is a 2:1 format bispecific antibody with two VHH arms targeting LILRB4 with high affinity and one scFv arm targeting CD3 with fine-tuned low affinity. The binding affinity of LBL-043 to LILRB4 and CD3 was determined with Fortebio, while the activity was measured using several cell based assays including reporter gene and TDCC assays. The anti-tumor activity of LBL-043 was investigated in B-NDG/hu-PBMC reconstructed mice implanted with MOLM-13 (human AML-M5a) tumor model. Results: The binding affinity of LBL-043 to LILRB4 and CD3 protein was 0.724 nM and 35.7 nM, respectively. In CD3 reporter gene assays, LBL-043 could activate the NFAT reporter signaling through LILRB4 binding dependent CD3 cross-linking with an EC50 value of 2.459 nM. LBL-043 was shown a potent TDCC activity in different LILRB4 expression level MOLM-13 cells and HL-60 cells with T cell activation and cytokine release. In B-NDG/hu-PBMC reconstructed mice implanted with MOLM-13 tumor cells, LBL-043 was shown significant anti-tumor activity. Simultaneously, LBL-043 can effectively improve the survival rate and maintain relatively stable body weight in the study compared to the vehicle group. Conclusion: LBL-043, a novel bispecific antibody targeting CD3 and LILRB4 with affinity differentiation, induces T cell killing of AML cells by simultaneously binding LILRB4 expressed on tumor cells and CD3 on T cells, redirecting T cells to efficiently killing of AML cells. It is also shown a great anti-tumor efficacy in CDX mouse models. These data support LBL-043 as a novel therapeutic bispecific antibody for the treatment of LILRB4 positive AML and CMML leukemia patients. Citation Format: Yujia Dang, Xiao Huang, Yurong Qin, Xiaoya Liu, Min Chen, Duqing Jiang, Guojin Wu, Mi Ye, Jianming Sun, Baohui Wang, Jing Guan, Tingting Li, Jordan Zhu, Shoupeng Lai, Xiaoqiang Kang, Hong Ling. LBL-043, a novel LILRB4xCD3 T cell engager, for the treatment of LILRB4 positive leukemia [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 6712.

Preparation of a dual-specific antibody targeting human CD123 and exploration of its anti-acute myeloid leukemia effects

Objective: To construct a novel dual-specific antibody targeting human CD123 (CD123 DuAb) and study its effects in acute myeloid leukemia (AML) . Methods: Based on the variable region of the CD123 monoclonal antibody independently developed at our institution, the CD123 DuAb expression plasmid was constructed by molecular cloning and transfected into ExpiCHO-S cells to prepare the antibody protein. Through a series of in vitro experiments, its activation and proliferation effect on T cells, as well as the effect of promoting T-cell killing of AML cells, were verified. Results: ① A novel CD123 DuAb plasmid targeting CD123 was successfully constructed and expressed in the Expi-CHO eukaryotic system. ②The CD123 DuAb could bind both CD3 on T cells and CD123 on CD123(+) tumor cells. ③When T cells were co-cultured with MV4-11 cells with addition of the CD123 DuAb at a concentration of 1 nmol/L, the positive expression rates of CD69 and CD25 on T cells were 68.0% and 44.3%, respectively, which were significantly higher than those of the control group (P<0.05). ④Co-culture with CD123 DuAb at 1 nmol/L promoted T-cell proliferation, and the absolute T-cell count increased from 5×10(5)/ml to 3.2×10(6)/ml on day 9, and CFSE fluorescence intensity decreased significantly. ⑤ With the increase in CD123 DuAb concentration in the culture system, T-cell exhaustion and apoptosis increased. When the CD123 DuAb was added at a concentration of 1 nmol/L to the culture system, the proportion of CD8(+) PD-1(+) LAG-3(+) T cells was 10.90%, and the proportion of propidium iodide (PI) (-) Annexin Ⅴ(+) T cells and PI(+) Annexin Ⅴ(+) T cells was 18.27% and 11.43%, respectively, which were significantly higher than those in the control group (P<0.05). ⑥ The CD123 DuAb significantly activated T cells, and the activation intensity was positively correlated with its concentration. The expression rate of CD107a on T cells reached 16.05% with 1 nmol/L CD123 DuAb, which was significantly higher than that of the control group (P<0.05). ⑦The CD123 DuAb promoted cytokine secretion by T cells at a concentration of 1 nmol/L, and the concentration of IFN-γ and TNF-α in the supernatant of the co-culture system reached 193.8 pg/ml and 169.8 pg/ml, respectively, which was significantly higher than that of the control group (P<0.05). ⑧When CD123 DuAb was added at a concentration of 1 nmol/L to the co-culture system of T cells and CD123(+) tumor cells, the killing intensity of T cells significantly increased, and the residual rates of CD123(+) MV4-11 cells, CD123(+) Molm13 cells, and CD123(+) THP-1 cells were 7.4%, 6.7%, and 14.6% on day 3, respectively, which were significantly lower than those in the control group (P<0.05) . Conclusion: In this study, a novel CD123 DuAb was constructed and expressed. In vitro experiments verified that the DuAb binds to CD123(+) tumor cells and T cells simultaneously, promotes T-cell activation and proliferation, and facilitates their anti-leukemia effect, which provides a basis for further clinical research.

Abstract P29: Zotatifin, the eukaryotic translation initiation factor 4A (eIF4A) inhibitor, synergizes with Venetoclax to inhibit acute myeloid leukemia cell growth

Abstract New targeted therapies such as the selective and potent BCL-2 inhibitor Venetoclax have revolutionized the treatment of acute myeloid leukemia (AML). However, due to the cellular heterogeneity of the disease, drug-resistant cell types often emerge and drive relapse. We found that the eukaryotic translation initiation factor 4A (EIF4A) is highly expressed in multiple primitive AML cell types compared to their healthy counterparts, suggesting its potential as a therapeutic target. By unwinding complex structures in the 5’ UTR of transcripts, eIF4A promotes the translation of oncogene transcripts. A first-in-class drug, Zotatifin, inhibits the helicase activity of eIF4A and curtails tumor growth in receptor tyrosine kinase-driven tumors. Zotatifin is currently being evaluated in phase 1/2 trials across multiple solid tumors (NCT04092673). However, its effectiveness in blood cancers such as AML remains unexplored, and it is unknown whether Zotatifin may work synergistically with Venetoclax. Here, we treated AML cell lines in vitro and primary healthy or AML bone marrow ex vivo with Zotatifin or Venetoclax alone and in combination, and demonstrate synergistic killing of AML cells by the combination therapy (ZIP synergy score = 57.0 in MOLM-13, 19.3 in MV4-11, P &amp;lt; 0.0001). Mechanistically, we show that Zotatifin decreases eIF4A and AKT expression, and its combination with Venetoclax drives increased BAK and cleaved BAK expression, as well as increased cleavage of MCL-1 and BCL-2, consistent with drug synergy by convergence on the apoptotic pathway. In pilot colony-forming unit (CFU) assays, we found the combination to be tolerable in healthy CD34+ human hematopoietic stem and progenitor cells (HSPCs). To test drug efficacy in vivo, we generated a patient-derived xenograft (PDX) AML model from a patient who experienced relapse with complex cytogenetics, FLT3 and NPM1 mutations. Only the combination of Zotatifin and Venetoclax but not monotherapies effectively suppressed tumor burden as assessed by human CD45 engraftment in the peripheral blood. Further, the combination of Zotatifin and Venetoclax significantly prolonged survival of xenografted mice (median survival after treatment: vehicle 11 days, Venetoclax 13 days, Zotatifin 15 days, combination 42 days, P = 0.0002). Together, our data indicates that Zotatifin is synergistic with Venetoclax and may represent an effective treatment option for patients who are either primary refractory or have developed resistance to existing Venetoclax-containing regimens. Citation Format: Yoke Seng Lee, Jonathan Good, Noha Awais, Benjamin Eschle, Jenny Noel, Jean Acosta, Erica DePasquale, David Cucchi, Prafulla Gokhale, Fadi Najm, Peter van Galen. Zotatifin, the eukaryotic translation initiation factor 4A (eIF4A) inhibitor, synergizes with Venetoclax to inhibit acute myeloid leukemia cell growth [abstract]. In: Proceedings of the Blood Cancer Discovery Symposium; 2024 Mar 4-6; Boston, MA. Philadelphia (PA): AACR; Blood Cancer Discov 2024;5(2_Suppl):Abstract nr P29.

Propionate promotes ferroptosis and apoptosis through mitophagy and ACSL4-mediated ferroptosis elicits anti-leukemia immunity

Short-chain fatty acids (SCFAs), particularly propionate and butyrate, have been reported in many cancers. However, the relationship between propionate and acute myeloid leukemia (AML) remains unclear. Additionally, Acyl-CoA synthetase long chain family member 4 (ACSL4) has been reported to regulate immunity in solid tumors, but there are still many gaps to be filled in AML. Here, we discovered the underlying mechanism of propionate and ACSL4-mediated ferroptosis for immunotherapy. Our results showed that the level of propionate in the AML patients’ feces was decreased, which was correlated to gut microbiota dysbiosis. Moreover, we demonstrated that propionate suppressed AML progression both in vivo and in vitro. In mechanism, propionate induced AML cells apoptosis and ferroptosis. The imbalance of reactive oxygen species (ROS) and redox homeostasis induced by propionate caused mitochondrial fission and mitophagy, which enhanced ferroptosis and apoptosis. Furthermore, ACSL4-mediated ferroptosis caused by propionate increased the immunogenicity of AML cells, induced the release of damage-associated molecular patterns (DAMPs), and promoted the maturation of dendritic cells (DCs). The increased level of immunogenicity due to ferroptosis enable propionate-based whole-cell vaccines to activate immunity, thus further facilitating effective killing of AML cells. Collectively, our study uncovers a crucial role for propionate suppresses AML progression by inducing ferroptosis and the potential mechanisms of ACSL4-mediated ferroptosis in the regulation of AML immunity.

Type 3 Innate Lymphoid Cells Promote Acute Myeloid Leukemia Immune Evasion and Expansion

Acute Myeloid Leukemia (AML) is an aggressive myeloid malignancy originated in the bone marrow with poor overall survival rates of less than 30%. The immune system has been shown to play an important role in detecting and eliminating leukemic cells. Recent studies have described a population of immune cells termed Innate lymphoid cells (ILCs). ILCs are known to regulate both innate and adaptive immunity in an antigen-independent manner and are believed to be among the first immune cells to interact with malignantly transformed cells. Natural killer (NK) cells are a subset of ILCs and are known to inhibit AML progression, however the impact of other ILCs is not yet fully understood. Type 3 ILCs (ILC3s) have key roles in maintaining homeostasis in mucosal immunity through their ability to secrete cytokines including IL-17, IL-22, TNFα and GM-CSF (pro-myeloid). An expansion of ILC3s has recently been observed in solid tumors, however the overall functional impact of ILC3s in the setting of AML remains poorly understood and warrants further investigation. We first utilized an MLL-partial tandem duplication and FLT3-internal tandem duplication Flt3-ITD double knock-in mutation murine model of AML that recapitulates two clinically relevant mutations in human AML. Using this AML model, we discovered an expansion of ILC3s in the bone marrow of leukemic mice compared to wild-type control mice (2.364% +/- 0.40% AML vs 0.045% +/- 0.40% WT, n=5, p&amp;lt;0.0001). We also observed an increase in ILC3s in the bone marrow of untreated AML patients relative to age matched donor controls (7.013% +/- 2.6% vs. 2.328% +/- 2.6%). Our published data have previously shown AML blasts secrete aryl hydrocarbon receptor (AHR) ligands, which can bind and activate the transcription factor AHR in ILC precursors and mature ILCs. AHR is an important transcription factor in ILC3 development. Therefore, we hypothesized that the ILC3 increase was due at least in part to AHR-mediated increased ILC3 differentiation. To address this hypothesis, we isolated the ILC precursor (ILCP) from normal human donors and co-cultured with AML cells. By regulating AHR activity in this system, we showed that ILC3s are expanded in AML in part due to AML-mediated AHR activation (28.02% +/- 3.89% without AML, 60% +/- 5.5% with AML and 27% +/- 5% AML+AHR inhibitor, n=15, p&amp;lt;0.001). Next, we sought to determine the direct impact of ILC3s on AML proliferation and differentiation that could contribute to AML relapse. We utilized a colony forming assay (CFU) assay in the presence or absence of ILC3s. Bone marrow from primary untreated AML patients was cultured alone or with ILC3s (Lin-CD94-NKp44+). AML samples co-cultured with ILC3s had significantly increased colony formation relative to AML alone (69.4 CFU AML+ILC3 vs 42.7 CFU AML alone, n=8, p&amp;lt;0.05). Post-culture, we observed significant increases in the transcript of GM-CSF and TNFα in ILC3s co-cultured with AML marrow as compared to ILC3s alone. Furthermore, in our immunocompetent murine AML model, we observed significantly higher production of GM-CSF and TNFα by ILC3s in the bone marrow of leukemic mice relative to nonleukemic controls (GM-CSF: 11.08% +/- 1.6 AML vs 1.128% +/- 1.6 WT, n=10, p&amp;lt;0.0001; TNFα: 5.456% +/- 1.3 AML vs 1.307% +/- 1.3 WT, n=10, p&amp;lt;0.05), suggesting a potential mechanism of ILC3-mediated increased colony formation. Lastly, to determine if ILC3 expansion impacted NK cell immune surveillance, we co-cultured normal donor human ILC3s with AML cells, separated by transwell, for 48 hours before subjecting the AML cells to an NK cell cytotoxicity assay. We observed significantly reduced NK cell killing of AML cells when co-cultured with ILC3s compared to controls, suggesting ILC3s protect AML cells from NK cell-mediated killing (24.3% killing +/- 3.81% AML alone vs 14.57% +/- 1.35% AML with ILC3, n=18, p&amp;lt;0.01). Collectively, these data support a model in which AML-mediated AHR activation promotes ILC3 expansion to both support AML proliferation and protect AML blasts from immune surveillance. Future studies will focus in exploring how to target these interactions to design effective therapeutic approaches and improve patient clinical outcomes.

TP53 Deficiency in AML Confers Resistance to CAR T-Cells That Can be Overcome By Targeting the Cholesterol or Wnt Pathways

Introduction TP53-mutant acute myeloid leukemia (AML) and myelodysplastic neoplasms (MDS) are distinct clinicogenomic entities characterized by chemotherapy resistance and high relapse rates after allogeneic stem cell transplantation, and thus, represent an unmet clinical need. Chimeric antigen receptor (CAR) T-cell therapy might be a promising therapeutic option for TP53-mutant AML/MDS. However, the AML-intrinsic determinants of response to T-cell-based approaches in AML, in particular the impact of TP53-deficiency, are largely unknown. In the present study, we addressed the biologically and clinically highly relevant question as to whether, and, if so, how TP53 deficiency in AML cells might confer resistance to CAR T-cell therapy. Results We took advantage of recently developed, CRISPR/Cas9-engineered TP53 isogenic AML cell lines harboring TP53 null, missense, or wildtype alleles to exclude other potential genetic confounders of therapy resistance. Flow cytometry-based co-culture assays using these isogenic cell lines together with CAR T-cells targeting the common AML surface antigens CD33, CD371, CD123, and CD117, showed that AML cells harboring TP53 null or missense mutations were relatively resistant to CAR T-cells in vitro. CAR T-cells engaging TP53-deficient leukemia cells proliferated less, upregulated exhaustion markers, displayed increased trogocytosis, and were ultimately unable to control AML cell outgrowth. Live-cell imaging revealed a longer engagement time of CAR T-cells with TP53-deficient AML cells before killing occurred as judged by propidium iodide influx. Immunodeficient mice xenografted with TP53-deficient AML cells and treated with CAR T-cells exhibited significantly shortened survival compared to TP53-wildtype AML controls. Transcriptional profiling revealed that the cholesterol pathway was upregulated in TP53-deficient AML cells under CAR T-cell attack. Simultaneously, CAR T-cells engaging TP53-deficient AML demonstrated a downregulated Wnt pathway, in particular the master regulators of T-cell fate TCF7 and EOMES. Rational pharmacological targeting of either of these pathways, blocking by Simvastatin and activation by BIO-acetoxime, respectively, rescued TP53-deficient AML cell sensitivity to CAR T-cell-mediated killing in vitro. Discussion and Outlook Using a combination of in vitro co-incubation assays, live-cell imaging, gene expression profiling and a therapeutic in vivo model we could demonstrate that TP53 deficiency in AML cells confers relative resistance to CAR T-cell therapy and elucidate some of the underlying molecular mechanisms in leukemia target cells and CAR T-cells. We thus propose a model, in which the intrinsic apoptotic defect in TP53-deficient AML/MDS cells results in a longer duration of the cellular interaction between CAR T-cells and TP53-deficient AML/MDS cells. This longer temporal interaction eventually leads to reduced CAR T-cell proliferation and enhanced CAR T-cell exhaustion with an overall decrease in AML cell killing (figure 1). Furthermore, we identified the cholesterol pathway as a potential therapeutic vulnerability of TP53-deficient AML cells engaged by CAR T-cells, and the Wnt pathway as a promising avenue to enhance the efficacy of CAR T-cell therapy in TP53-deficient AML/MDS. Our data suggest that the combination of CAR T-cell therapies with pharmacological co-interventions - as exemplified in this study - may be a preferable strategy towards more efficacious and tolerable cellular therapies for patients with TP53-mutant myeloid neoplasms.

Developing “Off-the-Shelf” CLL1 CAR-DNT Therapeutics for the R/R Acute Myeloid Leukemia

Background: Acute myeloid leukemia (AML) is one of the most common and highly heterogeneous hematological malignancy. The prognosis is poor especially for the elderly patients. For Relapsed/Refractory(R/R) AML patients, the one-year overall survival rate is merely 20%. CAR-T cells have shown tremendous therapeutic benefits for ALL, DLBCL and MM. One of the limitations of current CAR-T therapies is the use of autologous T cells. This can be limiting due to the cost, complicated manufacturing process, rapid disease progression, and manufacturing failures etc. Therefore, there is a need to develop the ready-to-use allogeneic cell product. Double negative T (DNT) cells are the ideal candidate for AML cell therapy as they naturally kill AML cells, and have been successfully administered to AML patients with therapeutic benefit without causing GvHD. Relying on their own natural immune activated receptors, DNT cells could lyse a wide range of tumors independent of TAA expression, which have more advantages compared to the conventional CAR-T cells. In our study, we developed the allogeneic product of CAR-DNT cells targeting C-type lectin-like molecule-1 (CLL1), which is a promising target due to its over-expression in primary AML cells and leukemia stem cells, while absence on hematopoietic stem/progenitor cells. Methods: We developed a humanized single chain variable fragment (scFv) with specific recognition of human CLL1 antigen by screening from 62 murine-derived CLL1 antibodies. Then, we designed a second-generation CLL1 CAR structure containing 4-1BB-CD3ζ and transduced it into the DNT cells by lentivirus. To clarify the GvH and HvG reactions of DNT cells, we performed the mixed lymphocyte reaction experiments in vitro and compared DNT cells with TCR and B2M double knockout T(DKO) cells and TCR knockout T(TKO) cells. We evaluated the anti-tumor function of CLL1 CAR-DNT cells through killing experiments by different effector-to-target ratios and multiple stimulations with AML cell lines (THP1 and HL60). Furthermore, we speculated that the CAR structure plays a critical role in both tumoricidal function and persistence of CAR-DNT cells. We designed nearly 20 enhanced CAR structures based on the signaling pathway of DNT cells. These newly designed structures have been tested in vitro and will be confirmed in vivo. Results: The humanized anti-CLL1 scFv candidate H1-3Q2 demonstrated high specificity toward human CLL1 antigen at the Membrane Protein Array. H1-3Q2 based CAR-T cells showed good tumor suppression in vivo. However, due to the heterogenous expression of CLL1 in AML, CLL1 CAR-T cells may not be able to eliminate AML cancer cells completely. While DNT cells could naturally lyse tumor cells through the receptors like NKG2D and DNAM-1, providing them with lots of advantages. Moreover, DNT cells have the potential to be used as allogenic cell therapy product. Co-culturing allogenic PBMCs or umbilical cord blood with DNT cells for up to 72 hours resulted in little or no killing reaction, indicated a low risk of GvHD. Conversely, the PBMCs from three different donors were used to attack allogenic DNT cells or DKO/TKO T cells in vitro. The killing effect on DKO/TKO T cells gradually increased over time, while no effect on DNT cells was observed even after 192 hours. This suggested that DNT cells are not easily cleared by host immune cells. DNT cells could efficiently lyse various hematological and solid tumor cell lines, particularly showing high sensitivity towards AML cells. The introduction of the CAR moiety further enhanced the specificity of DNT cells. The in vitro killing results demonstrated that CLL1 CAR-DNT cells exhibited stronger and faster AML resistance compared with CAR-T cells, and even eliminated tumor cells that have lost TAA. However, CLL1 CAR-DNT cells showed limited proliferation in the multiple-stimulation assays. To address this, we designed enhanced CAR structures. Screening by multiple-challenge assays, the fifth-generation CAR exhibited outstanding proliferation and superior tumor lysis ability in vitro. Conclusions: Our findings demonstrate that CAR-DNT product is an ideal candidate for allogeneic adoptive immunotherapy and exhibits superior tumoricidal function. This study underscores the potential of the “off-the-shelf” CLL1 CAR-DNT cell product for treating R/R AML.

Dose Escalation of HLA-A2-WT1 CD3 T-Cell Bispecific Antibody in a Phase I Study in Patients with Relapsed/Refractory Acute Myeloid Leukemia (AML)

Background: RO7283420 (RG6007) is a 2+1 TCR-like (TCR-L) T-cell bispecific (TCB) antibody targeting CD3 and the RMFPNAPYL peptide of Wilms Tumor 1 (WT1) protein presented by the major histocompatibility complex-I HLA-A*02 on acute myeloid leukemia (AML) blasts and other antigen presenting cells. The pre-clinical evaluation of RO7283420 in our in vivo humanized AML xenografts and ex vivo AML co-culture models showed strong T-cell mediated AML cell killing (Augsberger C, et al. Blood 2021). A Phase 1 dose-escalation (DE) study (NCT04580121) evaluated the safety, tolerability, pharmacokinetics, anti-drug antibodies (ADAs), and anti-leukemic activity of RO7283420 in patients with relapsed/refractory (R/R) AML. Methods: In this open-label, multi-center study, DE was performed using a 3+3 design. Patients received RO7283420 every 3 weeks (Q3W, n=46), or every week (QW, n=4) as intravenous (IV) infusions. Preliminary anti-leukemic activity included response assessment according to European Leukemia Net (ELN) response categories (adapted from Döhner H, et al. Blood 2017). Results: As of 13 April 2023, 50 HLA-A2+ R/R AML patients received at least one dose of RO7283420. Patients had a median age of 65.5 years (range 35-84), presented with ECOG of 0 (56%) or 1 (38%) or 2 (6%), and 58% were male. Median prior line of therapy was 2 (range 1-5). Overall, 58% of patients had relapsed and 42% had primary refractory disease. According to the ELN 2017 risk stratification, patients were of adverse (48%), intermediate (38%) or favorable (8%) risk category, for 6% of patients the risk category missing. The most common genetic abnormalities reported were RUNX1 (21%), ASXL1 (17%), TP53 (10.6%), FLT3-ITD (6.4%) and NPM1 (6.4%) of the 47 patients tested. Median bone marrow blast percentage at baseline was 35% (range 3-90%), while the median of circulating blast was 17% (range 0-88%). Study patients received RO7283420 IV at 13 different dose levels, ranging from a Minimum Anticipated Biological Effect Level (MABEL) of 0.15 mg (flat) to 18 mg Q3W (with a preceding weekly 1/3 mg ‘double step-up’ during Cycle 1) and one QW dose level with 9 mg preceded by a 1/3 mg step-up. Maximum tolerated dose was reached at 1/3/12 mg double step-up Q3W. Explored alternative QW schedule was not tolerable at 1/3/9 mg. The most common (≥20%) adverse events (AEs) were cytokine release syndrome (CRS) occurring in 34 (68%), pneumonia 14 (28%), pyrexia 13 (26%), febrile neutropenia 13 (26%), hyperglycemia 12 (24%), hypokalemia 11 (22%), and nausea 10 (20%) of patients. Eight dose limiting toxicities (DLTs) were reported: five G3 CRS (at 1/3, 2/12, 1/6/12 mg dose levels), G3 stomatitis (at 1/3/12 mg), G3 myositis (at 1/3/18 mg), and G4 thrombocytopenia (at 1/3/18 mg). Eleven patients (22%) experienced Grade 5 AEs with pneumonia, sepsis, and hemophagocytic lymphohistiocytosis (HLH) reported in &amp;gt;1 patient; all Grade 5 events were considered unrelated to RO728342 except 1 (at 1/3/9 mg) of 2 HLH events. IV PK has been overall dose-linear and characterized by a terminal half-life of 29 to 84 hours and a clearance of 58 to 92 mL/h. Preliminary ADA incidence within the study population was 19%. In the dose ranges tested, a trend for study drug exposure-dependent blast reduction was observed in blood, while a clear exposure-response relationship could not be established with BM blast reduction. Furthermore, our preliminary pharmacodynamic analysis identified expansion of naive and memory CD8 T cells in blood and activated CD8+ T cells in bone marrow, in line with the expected mode of action (MoA) of RO7283420. Preliminary efficacy signals were observed with 3 complete responses (CR), including 1 CR with incomplete blood count recovery. Conclusions: RO7283420 is the first TCR-L TCB antibody evaluated in AML. We observed pharmacodynamic evidence of T-cell activation and expansion in the clinic, in line with the expected MoA of TCBs, however, at the explored doses, no clear exposure-response relationship and only a modest clinical activity were observed. The safety profile was shown to be consistent with the other TCBs and R/R AML population. Based on the totality of data, the study was discontinued.

Novel CD123xCD3 Bispecific Igm Antibody, Igm-2537, Potently Induces T-Cell Mediated Cytotoxicity of Acute Myeloid Leukemia Cells In Vivo and in Vitro with Minimal Cytokine Release

Introduction: New therapeutics are needed for the effective treatment of acute myeloid leukemia (AML), as standard chemotherapeutics are poorly tolerated and ~50% of patients relapse primarily due to the incomplete elimination of leukemia stem cells (LSCs). CD123, the IL-3Rα chain, is highly expressed on leukemic blasts and LSCs, and is further increased in patients with poor prognostic factors. Bispecific T-cell engager (TCE) antibodies and CAR-T cells targeting CD123 have shown promising clinical efficacy in AML patients, but cytokine release syndrome limits their therapeutic window and remains a major safety concern. IGM-2537 is a novel pentameric IgM bispecific TCE antibody engineered with ten anti-CD123 binding sites, and an anti-CD3ε single chain Fv domain fused to the joining chain to engage T-cells. Here, we report that IGM-2537 not only potently induces T-cell mediated cytolytic killing of AML cells in vitro and in vivo but also demonstrates minimal cytokine release, and little to no effect on normal hematopoietic progenitor cells and human vascular endothelial cells (HUVECs) with in vitro and ex vivo studies. Additionally, an improved tolerability, excellent pharmacodynamic (PD) response and lower cytokine release was observed with a cynomolgus cross-reactive IgM TCE in monkeys. Materials and Methods:Surface plasma resonance (SPR), cell membrane protein array, and alanine scanning were utilized to characterize human CD123 binding affinity, specificity and epitope mapping, respectively. T-cell dependent cellular cytotoxicity (TDCC) assays were employed to evaluate the potency of IGM-2537 target cytotoxicity, T cell activation and cytokine release. Ex vivo AML colony formation assays were used to assess the activity on AML blasts. Human MV-4-11 and MOLM-13 xenograft tumor models in humanized NSG dKO mice were utilized to determine in vivo anti-tumor activity of IGM-2537. Healthy human PBMCs and bone marrow (BM) samples as well as HUVECs were used in ex vivo assays to address potential safety concerns of IGM-2537 mediated effects on hematopoietic progenitor cells and HUVECs, respectively. Lastly, to confirm that a CD123 directed IgM-based TCE molecule can potentially provide better safety profile in vivo, a cynomolgus-cross reactive IgM TCE comparator was assessed in monkeys for tolerability and PK/PD responses. Results and Conclusions: IGM-2537 bound with high affinity and avidity to CD123. In vitro, IGM-2537 engaged both CD123 and CD3 to induce potent T-cell activation and T-cell mediated cytotoxicity of CD123 + AML cells, and autologous CD123 + basophils and plasmacytoid dendritic cells (pDCs). Though IGM-2537 demonstrated comparable maximal killing activity to a comparator IgG TCE, IGM-2537 demonstrated minimal cytokine release. In ex vivo patient-derived AML or normal BM colony formation assays, IGM-2537 eliminated AML colony forming cells at physiologically relevant effector/target (E/T) ratios but had little or no effect on normal hematopoietic progenitors. In addition, IGM-2537 demonstrated no cytotoxicity against HUVECs regardless of their CD123 expression at basal levels or at maximal levels upregulated by TNF-a and IFN-g, in contrast to a comparator IgG TCE. In vivo, IGM-2537 completely inhibited tumor growth in two AML xenograft tumor models, a subcutaneous MV-4-11 model, and a systemic MOLM-13 model in humanized NSG dKO mice. To further evaluate the potency and safety of the CD123xCD3 IgM bispecific TCE format in vivo, a cynomolgus cross-reactive CD123xCD3 IgM bispecific TCE was evaluated for tolerability and PD responses in cynomolgus monkeys using single doses. All animals tolerated the cross-reactive bispecific IgM TCE well at doses up to 10 mg/kg (the maximal dose level evaluated), a dose 100-fold greater than published doses of a comparator IgG TCE. Complete depletion of CD123 + basophils and substantial reductions of pDCs were seen in blood and BM with minimal to no cytokine induction. In summary, IGM-2537 demonstrated potent in vitro and in vivo T-cell mediated cytotoxicity of AML cell lines with minimal cytokine induction. The encouraging preclinical safety profiles were further supported by little/no effect on normal hematopoietic progenitor cells and HUVECs. These preclinical data support the clinical development of IGM-2537 for the treatment of AML and other hematological malignancies.

Co‐Targeting c‐Myc and Bcl‐2 by Oral Small Molecule Combination of WBC100 and Venetoclax Effectively Controls Acute Myeloid Leukemia in Preclinical Models

AbstractUncontrolled proliferation and apoptosis evasion are two hallmarks of acute myeloid leukemia (AML), but the molecular mechanisms remain poorly understood. In this study, it is demonstrated that the double over‐expresser of oncoprotein c‐Myc and anti‐apoptotic protein Bcl‐2 is a critical “genetic overdrive” of proliferation and apoptosis evasion in AML and is associated with poor genetic alterations. Double‐knockdown of c‐Myc/ Bcl‐2 synergistically kills AML cells in vitro and in vivo. Moreover, a novel oral small molecule combination co‐targeting c‐Myc and Bcl‐2 with WBC100 and Venetoclax (VEN) at low doses are developed. Importantly, the study shows that this combination results in deep and durable remissions of AML, and its efficacy is superior to the frontline combination of Venetoclax and hypomethylation azacitidine (AZA) in AML mouse models and PDX models from relapsed or refractory AML patients. Mechanically, Bcl‐2 knockdown induces mitochondrial outer membrane permeabilization and c‐Myc‐knockdown impairs mitochondria biogenesis. Co‐targeting c‐Myc/Bcl‐2 reciprocally abrogates over‐proliferation and apoptosis resistance via forming a double hit to mitochondrial biogenesis and apoptosis machinery. The findings for the first time demonstrate that co‐targeting c‐Myc/Bcl‐2 by the novel oral small molecule combination of WBC100/Venetoclax is a promising and convenient therapy for AML and support its clinical trial.

A phase 1/2 dose escalation study of the BCL-2 inhibitor ZN-d5 and the WEE1 inhibitor azenosertib (ZN-c3) in patients (Pts) with acute myeloid leukemia (AML).

TPS7077 Background: B-cell lymphoma 2 (BCL-2) is an anti-apoptotic protein and pathway inhibition combined with chemotherapy and/or targeted therapeutics has led to significant clinical benefit in pts with AML. Disruption of cell cycle regulation may complement BCL-2 inhibition as many malignant cells are dependent on proteins that regulate cell cycle progression. The cell cycle checkpoint protein, WEE1, is highly expressed in genomically unstable malignancies and inhibition of WEE1 induces tumor cell apoptosis. It has been previously reported that the combination of ZN-d5 (an oral, selective BCL-2 inhibitor) and azenosertib (an oral, highly potent WEE1 inhibitor) synergistically enhance killing of AML cells both in vitro and in vivo, as well as in TP53-mutated models (Izadi, AACR 2022). Based on this strong pre-clinical rationale, a Phase 1/2 study was designed to evaluate the novel combination of ZN-d5 and azenosertib in pts with relapsed/refractory (R/R) AML. Methods: This phase 1/2 open-label study (ZN-d5-004C, NCT05682170) is determining the maximum tolerated dose (MTD), recommended phase 2 dose (RP2D), pharmacokinetics (PK), and clinical activity of ZN-d5 + azenosertib in pts with AML. The phase 1 dose-escalation stage is based on a Bayesian Optimal Interval design. Phase 2 is an open-label expansion to be conducted if supported by safety and efficacy data from the dose-escalation stage. Prior to initiating dose-escalation for the ZN-d5 + azenosertib combination, an azenosertib monotherapy cohort is being enrolled, as it has not been previously administered to pts with hematologic malignancies. For the dose-escalation azenosertib monotherapy (n≈15) and ZN-d5 combination (n≈40) cohorts, pts must have relapsed/refractory (R/R) disease after ≥1 line of AML therapy that may include the BCL-2 inhibitor, venetoclax. In phase 1, an azenosertib monotherapy cohort will be opened prior to investigation of ZN-d5 + azenosertib in combination. In phase 2, ZN-d5 + azenosertib will be given at the RP2D. Alternative dosing schedules may also be investigated based on emerging clinical data. The primary endpoints are adverse events and dose-limiting toxicities. Secondary endpoints include the rate and duration of remission according to the European LeukemiaNet 2017 criteria, including complete remission (CR), CR with incomplete hematologic recovery (CRi), morphologic leukemia-free state (MLFS), partial remission (PR), stable disease, progressive disease, relapse after remission (including molecular relapse), remission rate (CR + CRi), overall response rate (CR + CRi + MLFS + PR), and rate of and time to relapse. Pts will remain on study until disease progression, failure to respond, remission if additional therapy is clinically indicated, withdrawal of consent, loss to follow-up, or death. Clinical trial information: NCT05682170 .

DNA damage to bone marrow stromal cells by antileukemia drugs induces chemoresistance in acute myeloid leukemia via paracrine FGF10–FGFR2 signaling

Chemo-resistance remains a major challenge in the current treatment of acute myeloid leukemia (AML). The bone marrow microenvironment (BMM) plays a complex role in protecting leukemia cells from chemotherapeutics, and the mechanisms involved are not fully understood. Anti-leukemia drugs kill AML cells directly but also damage the BMM. Here, we determined anti-leukemia drugs induce DNA damage in bone marrow stromal cells (BMSCs), resulting in resistance of AML cell lines to adriamycin and idarubicin killing. Damaged BMSCs induced an inflammatory microenvironment through NF-κB; suppressing NF-κB with small molecule inhibitor Bay11-7082 attenuated the pro-survival effects of BMSCs on AML cell lines. Furthermore, we used an ex vivo functional screen of 507 chemokines and cytokines to identify 44 proteins secreted from damaged BMSCs. Fibroblast growth factor-10 (FGF10) was most strongly associated with chemo-resistance in AML cell lines. Additionally, expression of FGF10 and its receptors, FGFR1 and FGFR2, was increased in AML patients after chemotherapy. FGFR1 and FGFR2 were also widely expressed by AML cell lines. FGF10-induced FGFR2 activation in AML cell lines operates by increasing P38 MAPK, AKT, ERK1/2, and STAT3 phosphorylation. FGFR2 inhibition with small molecules, or gene silencing of FGFR2 inhibited proliferation and reverses drug-resistance of AML cells by inhibiting P38 MAPK, AKT, and ERK1/2 signaling pathways. Finally, release of FGF10 was mediated by β-catenin signaling in damaged BMSCs. Our data indicate FGF10-FGFR2 signaling acts as an effector of damaged BMSC-mediated chemo-resistance in AML cells, and FGFR2 inhibition can reverse stromal protection and AML cell chemo-resistance in the BMM.

Generation Natural Killer Cell-Mimic Nanoparticles for Active Targeting of Acute Myeloid Leukemia

Natural killer (NK) cells play a crucial role in recognizing and killing emerging tumor cells. Via an array of activating and inhibitory receptors, NK cells can target and kill abnormal cells, including tumor cells, without prior antigen sensitization. However, fully-established tumors employ numerous mechanisms to inactivate NK cells or hide from them, for example by shedding NK cell-activating ligands, like NK2GD (Chiossone et al., 2018). Here, we describe the engineering of nanoparticles (NPs) functionalized with tumor-recognizing and cytotoxic components of NK cells to address this problem and develop a nanoparticle-based treatment strategy simulating NK cell functionality. Liposomes were synthesized using the thin film hydration method followed by extrusion and functionalized them with the death ligand, TRAIL (tumor necrosis factor-related apoptosis-inducing ligand), immunoglobulin Fc-binding peptide (FCP, replicating the function of NK CD16 receptor) and the therapeutic antibody, anti-CD38 (daratumumab, Panel A) to target acute myeloid leukemia (AML). Transmission electron microscopy (TEM) and dynamic light scattering (DLS) were used to monitor morphology and size of liposomes. The potential of NK cell-mimic NPs (CD38-NK.NPs) to target and kill AML cells was evaluated on primary AML blasts and a disseminated AML xenograft for which the CD38-positive AML cell line, OCI-AML2 was engrafted into 8-9 week-old female NSG mice. Upon establishment of AML, the mice were injected intraperitoneally (i.p) with 5 doses of either naked liposomes (as vehicle control), soluble TRAIL protein (sTRAIL), LP/TRAIL or CD38-NK.NPs every two days. Tumor burden was monitored by determining the frequency of live human CD45+ cells in the peripheral blood, spleen and bone marrow with flow cytometry. Liposome was chosen as the base of the NP due to its high biocompatibility, biodegradability, cell-like characteristics and capability to penetrate through vessel walls (Pattni, Chupin and Torchilin, 2015). TEM and DLS measurements showed the generated NK.NPs were monodisperse with an average diameter of 145 nm, a size enabling vessel transmigration and avoiding kidney filtration (Gaumet et al., 2008). Immunofluorescent labelling of TRAIL, FCP and antibody verified CD38-NK.NPs functionalization. In vitro, both TRAIL-conjugated liposomes and CD38-NK.NPs were more effective in killing AML cell lines (ML-1, ML-2, Kasumi-1, and OCI-AML2) than sTRAIL, indicating that TRAIL-mediated cytotoxicity can be enhanced by presenting TRAIL in a conformation close to its membrane-bound structure. No significant difference could be detected between LP/TRAIL vs. CD38-NK.NP cytotoxicity in the in vitro assays. On the other hand, CD38-NK.NPs were more effective in killing primary AML blasts than non-targeted, NP-conjugated TRAIL (LP/TRAIL, 13±17% vs 4±15% killing, respectively). Moreover, CD38-NK.NPs showed considerably higher activity relative to the NK cell line, KHYG-1, against CD38-positive AML cell lines. Notably, CD38-NK.NPs showed no significant cytotoxic effect on non-malignant peripheral blood leukocytes. In vivo, NK cell-mimic NPs were more efficient in targeting and eradicating CD38-positive AML cells that either sTRAIL or LP/TRAIL, shown by the reduced percentage of circulating hCD45+ AML cells in treated mice (Panel B). CD38-NK.NPs were also more efficient in inhibiting accumulation of AML cells in the bone and spleen than sTRAIL and LP/TRAIL (Panel B), confirming the ability of CD38-NK.NPs to actively target AML cells expressing the targeted biomarker. Of note, CD38-NK.NPs showed no detectable systemic toxicity or damage to kidneys, liver and pancreas in healthy NSG mice. Overall, we have developed an NK cell-mimic nanoparticle able to actively target AML based on AML surface marker expression without any detectable systematic toxicity. Importantly, due to the modular built of the NK.NPs, they can be functionalized by any therapeutic tumor-targeting antibody via the immunoglobulin-binding peptide (FCP), thus enabling selective targeting tumor cells based on expression of tumor-specific markers and enabling personalized therapy. Figure 1View largeDownload PPTFigure 1View largeDownload PPT Close modal

MP0533: A Multispecific Darpin CD3 Engager Targeting CD33, CD123, and CD70 for the Treatment of AML and MDS Designed to Selectively Target Leukemic Stem Cells

Introduction: Acute myeloid leukemia (AML) is driven by leukemia stem cells (LSCs) that resist conventional chemotherapy and are the major cause of relapse. Newer therapies, including chimeric antigen receptor (CAR) T cells and T cell engagers (TCE) that target specific tumor associated antigens (TAAs) overexpressed on stem cells and leukemic blasts, are promising options for AML. We postulated that a TCE able to simultaneously target multiple TAAs could allow highly efficient and specific T cell-mediated killing of AML LSCs and circulating blast cells while minimally affecting healthy cells. Moreover, the simultaneous targeting of different TAAs has the potential to address tumor heterogeneity, allowing targeting of AML cells with different co-expression patterns and/or expression levels of each TAA. Methods: Our DARPin (Designed Ankyrin Repeat Protein) libraries contain trillions of molecules allowing the generation of highly diverse binders against target proteins that can be easily combined into multi-specific DARPins to elicit desired biological effects. We leveraged this proprietary platform to screen multi-specific CD3 engaging DARPin molecules, including serum albumin binding DARPins for systemic half-life extension, to generate MP0533, the first half-life extended avidity-engineered CD3 engaging DARPin capable of targeting CD33, CD123, and CD70 simultaneously. Efficacy and safety of MP0533 was extensively tested in vitro and ex vivo, with cell lines and primary cells in both allogenic and autologous settings, and in vivo in different cell line-derived xenograft mouse models. Results: We demonstrated the avidity effect of the multi-targeting MP0533 in co-culture assays with genetically engineered Molm-13 cells and allogenic T cells, where MP0533 induced up to 10-fold higher T cell mediated killing of cells expressing any combination of at least 2 of the 3 targeted TAAs vs. cells expressing a single TAA. Overall, an EC50 potency ranging from 5 to 25 pM was measured on multiple cell lines showing different levels of expression and co-expression of all TAAs (Molm-13, THP-1, RPMI8226). Efficacy was additionally assessed on primary unsorted AML bone marrow samples: MP0533 demonstrated the ability to induce autologous T cell activation and killing of AML cells in samples from newly diagnosed and previously treated patients with different TAA expression/co-expression levels and E:T ratios ranging from 10:1 to 1:28. MP0533-induced killing of LSC and selectivity over healthy hematopoietic stem cells (HSCs) was analyzed in clonogenic assays in co-cultures of sorted CD34+ cells with allogenic T cells. After 4 days initial killing assay, and 2 weeks colony culture in semi-solid media, MP0533 was able to show depletion of LSC at doses where HSC where only minimally affected. While T-cell activation, proliferation, and cytotoxicity were not affected, the multi-specific TCE format of MP0533 resulted in a significant decrease in cytokine release in both tumor cell killing assays and whole blood test systems when compared to other mono-targeting TCEs, indicating potential for improved safety. Moreover, the avidity approach and the safer profile on single-TAA expressing cells was confirmed by the absence of toxicity measured on CD123-expressing endothelial cells, indicating a low risk of capillary leak syndrome induced by MP0533. Also, potential T cell fratricide induced by CD70 expression on activated T cells was not observed. Finally, efficacy and safety profiles were also confirmed in in vivo xenograft models in human PBMC- or CD34-reconstituted mice. In such models MP0533 induced T cell infiltration in s.c. implanted tumors, leading to anti-tumor activity. Importantly, activation of T cells and release of cytokines were only localized in the tumors, indicating absence of potential systemic on-target off-tumor toxicities induced by MP0533. Conclusion: We generated a multi-specific avidity-driven CD3 engaging DARPin molecule with tailored affinities towards different TAAs showing high efficacy and with the potential for better LSC selectivity and lower cytokine release compared with mono-specific TCE approaches. Further, our approach to achieve systemic half-life extension could ensure a more convenient Q1W IV therapy. A Phase I clinical trial to evaluate safety and dose of MP0533 in humans is imminent.

Spatially Confined T-Cell Mediated Anti-AML Tumor Immunity By Dual Recognition Antibodies (CD123/CD200)

Definitive cure of acute myeloid leukemia (AML) remains an unmet need. While recombinant antibody-based and CAR-T cell mediated immunotherapies bear great potential in targeting chemotherapy-resistant leukemic stem cells, these approaches are largely limited by the lack of specific targets uniquely expressed by leukemic cells. Here, we propose a combinatorial strategy using a two-target approach which may have improved on-target and reduced off-target effects. The well-known stem cell marker interleukin-3 receptor α (CD123) is expressed on most AML cells. CD200 recently emerged as a cell surface marker mediating immuno-evasion on high-risk AML cells. We engineered the "Prodrug-activating chain Exchange"(PACE) TriFAB system (Dickopf S et al. Biological Chemistry, 2022) to yield a combinatorial anti-AML directed T-cell response. PACE-TriFAB educts are complementary Knob-into-hole IgG derived prodrugs in which one half is exchanged by a dummy containing an interface destabilizing mutation in the CH3 domain. The CH2 domain of the main body is replaced by a CD3 FAB light or heavy chain, respectively. With the hinge region being replaced by a flexible linker and therefore lacking disulfide bonds, a chain exchange between two educts is enabled when in close proximity on the cell surface. This leads to an activated anti CD3 domain and a dummy-dummy by-product. To demonstrate the T-cell activating potential, we co-cultured fresh PBMCs from healthy donors together with the CD200+/CD123+ AML cell line Kasumi-1 and checked T-cell activation by flow cytometry (E:T ratio 5:1, prodrug conc. 20 nM, 24 h stimulation). We observed a marked increase in CD69, CD25 and CD137 expression on CD8+ cells in the case when the CD123 and CD200 prodrugs were applicated simultaneously together with target cells, but not when single prodrugs alone or without target cells were analyzed (Median fluorescence intensity for CD25, CD69 and CD137: No construct: 450, 8.900 & 2.100; prodrug CD200: 460, 8.700 & 2.100; prodrug CD123: 460, 9.600 & 2.000; both prodrugs: 6.500, 344.300 & 43.100; results confirmed in repeat experiments) For the evaluation of the specific cytotoxic effect of the construct we transduced Kasumi-1 cells with an mCherry lentiviral vector and imaged the cells co-cultured with PBMCs every 2 h over a time span of 60 h (E:T ratio 5:1, prodrug conc. 10 nM). Proliferation of the Kasumi-1-mCherry cells was observed when no prodrug or only a single prodrug was added. However, application of both prodrugs together led to a decrease in mCherry positive cell count (log2 fold changes to starting point: No PBMCs 1,2; no construct 0,9; prodrug CD200 0,9; prodrug CD123 0,4; both prodrugs -2,1; n=3). Not only could we show that this elimination of tumor cells was dose dependent but also it was constrained by the E:T ratio (pivot point from killing to proliferation at 0,1 nM and E:T of 1:2 n=3). Similar results were obtained using patient derived xenograft (PDX) AML cells. In contrast to Kasumi-1 AML cells, specific killing of patient-derived PDX cells could be documented with lower E:T ratios and lower prodrug concentrations (pivot point from killing to proliferation at 0,05 nM and E:T of 1:5) We also started to analyze the anti-leukemic effect in vivo. Luciferase-expressing CD200+/CD123+ AML PDX cells were injected into NSG mice. On day +15, PBMC from a healthy individual were transplanted, followed by additional applications of the antibodies on days +16, +18, +21, +23, +25 & +29. Tumor burden was analyzed by bioluminescence imaging (log10 fold change [P/sec] 2 weeks after PBMC injection: Control 1,9; treated -0,4; group size = 3). In conclusion the combination of anti CD200 and anti CD123 as prodrugs of an on-target activating trispecific T-cell engager kills AML cells in vitro and in vivo and has the potential to eliminate AML LSC while minimizing the risk for severe on-target off-leukemia toxicity. Figure 1View largeDownload PPTFigure 1View largeDownload PPT Close modal